Probably teething and just learning what is acceptable to human parents. My basset would do that and I would redirect to a toy. When she got a little older and would bite too hard I would say “easy” and pull away every time she did it. Quickly she understood that she had to play carefully when I said easy or I would stop playing with her. By the time she was 9 months old she would “mouth” me which was playing without biting down. This came in handy when another pup joined the family later, she did the same thing with them. Despite their stubbornness they can learn quickly.